This invention relates to a clutch system of the friction type placed in a power transmission system. Typical clutch systems include a clutch input such as a clutch basket, a clutch output such as a center clutch, and one or more plates making up a clutch pack and disposed between the clutch input and clutch output. When the clutch pack is compressed, the clutch input and clutch output become rotationally coupled. The clutch pack is typically compressed by a pressure plate; the pressure plate typically providing a compressive force via a spring mechanism or through a centrifugally actuated mechanism. Most clutch systems can be disengaged by means of a lever acting on a clutch throwout which pushes the pressure plate away from clutch pack, rotationally decoupling the clutch input and clutch output.
Most motorcycles incorporate a clutch system whose clutch pack includes multiple driving friction plates and driven plates. The driving friction plates are typically formed from aluminum with friction material bonded to both sides of the plate. The driving friction plates are typically coupled rotationally with the clutch basket. Driven plates are typically formed from steel and are typically coupled rotationally with the center clutch.
Most motorcycles incorporate a clutch basket that is formed from aluminum. Aluminum is inexpensive to cast and lightweight relative to other materials such as steel. However, one disadvantage of aluminum for constructing a clutch basket is that it is soft relative to other materials such as steel. Significant wear at the surfaces on the clutch basket where the driving friction disks engage the clutch basket is a common problem.
One problem with forming the driving friction plates from aluminum is heat storage and heat expansion. When the clutch slips, during take-off for example, heat is generated. The driving friction plates and driven plates absorb this heat until the heat can dissipate out of the clutch system. If the clutch slips excessively, the heat build-up can be significant; causing the clutch pack to expand. When the clutch pack expands from heat, the pressure plate is pushed away from the clutch throwout; requiring more lever movement to rotationally decouple the clutch input and clutch output. This phenomenon is known as “clutch fade”.
It is well known that steel, by volume, has more thermal capacity and a lower thermal coefficient of expansion than aluminum. By forming the friction plate from steel instead of aluminum, given the same amount of slip and therefore the same amount of heat generation, a clutch system incorporating driving friction disks formed from steel will have reduced “clutch fade” vs. a clutch system incorporating driving friction disks formed from aluminum.
However, steel is typically much harder than aluminum. When a driving friction disk formed from steel is used in place of a driving friction disk formed from aluminum, wear at the surfaces on the aluminum clutch basket where the driving friction disks engage the clutch basket is accelerated.
The KTM 2006 450 SXF motorcycle model uses driving friction plates formed from steel and a clutch basket formed from steel. The KTM motorcycles are considered a premium brand and are generally more expensive than similar motorcycles from other manufactures. Most modern motorcycles use driving friction plates and a clutch basket formed from aluminum.
One way to overcome the problem of excessive wear of the clutch basket from the driving friction plates is to form the clutch basket from a harder, more wear resistant material such as steel. However, forming a clutch basket from steel would increase its weight and likely its cost versus a clutch basket formed from aluminum. A lightweight clutch basket is advantageous in that it has less reciprocating mass; allowing for quicker acceleration than a heavier clutch basket.
Typically the driving friction plates wear out and are replaced several times before the clutch basket is replaced due to wear. Requiring the owner of a vehicle to purchase a new clutch basket to prevent rapid wear from the use of improved driving frictions plates formed from steel is undesirable for both cost and increased weight of the clutch basket.
Steel is also stronger than aluminum. Forming the driving friction plate from steel allows the use of a driving friction plate that is thinner than a comparable aluminum driving friction disk and having the same strength. It is well known that by using more driving friction plates in a clutch system that the clutch system will have greater torque capacity assuming equal spring pressure. However, a thinner driving friction plate will have even greater wear characteristics against a relatively soft clutch basket due to the reduced surface area at the point of engagement with the clutch basket.
Taylor in U.S. Pat. No. 7,287,632 and Martin in U.S. Pat. No. 6,708,807 have proposed using liners, formed from a hard material such as steel, between the clutch basket and the driving friction plates to reduce wear and provide a replaceable wear surface. Both U.S. Pat. Nos. 7,287,632 and 6,708,807 are included herein by reference. Such a liner could be very advantageous in use, especially when combined with driving friction plates formed from steel. However neither Taylor nor Martin have proposed a liner that could easily be adapted by the owner of the vehicle to most common existing clutch baskets. Martin proposes a liner that slides into place without fasteners or adhesives but requires a clutch basket that was designed to accept the liner. Most common existing clutch baskets were not designed to accept a liner such as proposed by Martin. The liner disclosed by Martin requires a clutch basket with substantially recessed planar inner edges and recessed planar outer edges including a well-defined distance between the edges to capture U-shaped retaining clips on each leg. Most modern motorcycle clutch baskets are formed with an inner diameter and an outer diameter. Furthermore, the distance between the inner and outer diameter of the clutch basket varies greatly between clutch basket models. A liner solution that requires retention on the outer and inner diameter will not work on a wide variety of clutch baskets.
Taylor proposes a liner that could be adapted to most common existing clutch baskets but requires some form of adhesive or fastener to hold the liner in place. Securing the liners proposed by Taylor with an adhesive or a fastener is not something that most vehicle owners will be easily capable of doing. Typically, this operation would need to be performed by a specialized repair or remanufacturing facility or be manufactured as part of the original clutch basket. Furthermore, at least some of the liners disclosed by Taylor adapt to and engage both the inner and outer diameter of the clutch basket. Typically many different vehicles from many different manufactures will use a friction disk of the same dimensions. This requires the interior features of the clutch basket to be very similar between many different manufacturers. However, the exterior features of the basket tend to be different between different manufactures because the driving friction disks do not locate on the exterior features. Furthermore, there is often very limited space between the outer diameter of the clutch basket and the engine case; in many cases, a liner covering the outer diameter of the clutch basket could interfere with the engine case.
Therefore, a need exists for an improved liner for a vehicle's existing clutch basket that can easily be installed by the vehicle owner, without special tools or adhesives. A need exists for the liner to be restrained from radial outward movement by the inner diameter of the clutch basket so as to work with the stock clutch basket supplied with most modern motorcycles. The improved liner should provide improved wear resistance to the clutch basket driving friction plate engagement surfaces; especially when used in conjunction with a driving friction plate formed from steel or other material that has increased wear properties against the vehicle clutch basket. Furthermore, a need exists for a clutch pack system with improved resistance to heat induced “clutch fade”, that will easily retrofit into a vehicle's existing clutch system without imposing increased wear on the clutch basket's driving friction plate engagement surfaces. The improved clutch pack's friction disk should incorporate a clutch basket engagement tab with reduced width versus the standard friction disk so as to fit in the narrowed space provided by the improved liner.
Heretofore, no one has proposed a liner system than can easily be adaptable by a typical vehicle owner to an existing typical vehicle standard clutch basket, without fasteners or adhesives. Furthermore, no one has proposed a friction disk system whose driving friction plates are formed from a material that offers improved thermal heat capacity vs. the original driving friction plates and that can be retrofitted into an existing clutch basket that is formed from a material softer than the improved friction disk material, without creating accelerated wear on the clutch basket's driving friction plate engagement surfaces and that includes a clutch basket engagement tab with a reduced width to fit within the narrowed slot space provided by the improved liner.
Therefore, it is one object of the invention to provide a friction disk system with improved thermal properties and less thickness than a standard aluminum friction disk that can operate within a standard clutch basket without accelerating the wear of the standard clutch basket in operation. It is another object of the invention to provide a liner system that can easily be retrofitted to a clutch basket that was not designed to use a liner system, without the need for special tools or fasteners. It is another object of the invention to provide the improved liner system in conjunction with a friction disk system with improved thermal properties and less thickness and formed with clutch basket engagement tabs whose width is selected to fit inside the narrowed space provided by the improved liner system.
A preferred embodiment of the present invention is shown in FIGS. 1 through 5.